This application is based on Application No. 2001-48363, filed in Japan on Feb. 23, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an ignition timing control apparatus for an internal combustion engine provided with a swirl control element for adjusting the magnitude or momentum of an intake air swirl according to engine operating conditions, and more particularly, it relates to such an ignition timing control apparatus for an internal combustion engine capable of preventing knocks from occurring immediately after an intake air control valve is driven to operate.
2. Description of the Related Art
In the past, it has been proposed that in an ignition timing control apparatus for an internal combustion engine, provision is made for a swirl control element for adjusting the magnitude or momentum of an intake air swirl in accordance with the operating conditions of the engine.
Such a kind of ignition timing control apparatus for an internal combustion engine is described in Japanese Patent Publication No.7-42916, for example. The apparatus disclosed therein sets ignition timing in accordance with the engine operating conditions including the operating state of an intake air control valve.
In addition, there has also been known another apparatus in which ignition timing data for an open state and a closed state, respectively, of an intake air control valve are set in advance so that they are switched over in accordance with the operating state of the intake air control valve.
In general, in an internal combustion engine equipped with a low-load intake air passage and a high-load intake air passage, the low-load intake air passage and the high-load intake air passage are switched from their open state to their closed state or vice versa in accordance with the engine operating conditions.
That is, when the engine is operating under a low load, the high-load intake air passage is closed to increase the magnitude or momentum of a swirl of intake air, thereby improving combustion efficiency and fuel economy, whereas when the engine is operating under a high load, the high-load intake air passage is opened to decrease intake air resistance, thus providing high power.
At this time, the burning rate of an air fuel mixture is higher when the momentum of the intake air swirl is strong than when the momentum of the intake air swirl is weak, and hence it is necessary to retard the ignition timing at a high burning rate. Accordingly, there has been proposed an apparatus which is capable of switching the settings of ignition timing corresponding to the opening and closing of an intake air control valve, as described above.
FIG. 5 is a block diagram illustrating a common ignition timing control apparatus for an internal combustion engine, which is applied to an automotive engine control apparatus for example. In FIG. 5, an intake pipe 3 with an air cleaner 2 attached at one end thereof is connected at the other end thereof with an internal combustion engine (hereinafter simply referred to as xe2x80x9cenginexe2x80x9d) 1 through a surge tank 4 and an intake manifold 5, so that air is sucked into the engine 1 through the air cleaner 2, the intake pipe 3, the surge tank 4 and the intake manifold 5.
Mounted on the intake pipe 3 is a throttle valve 6 which is associated with an unillustrated accelerator pedal or lever so that the throttle valve 6 is operated by or in synchronization with the accelerator pedal or lever.
An exhaust pipe 7 is connected at its one end with the engine 1, and a catalytic converter 8 is inserted in the exhaust pipe 7 for purifying exhaust gases discharged from the engine 1. Thus, the exhaust gases generated by combustion of an air fuel mixture in the engine 1 are purified by the catalytic converter 7 and discharged to the ambient atmosphere through the exhaust pipe 6.
An electronic control unit (hereinafter simply referred to as xe2x80x9cECUxe2x80x9d) 10, which constitutes an engine controller proper for the engine control apparatus, is comprised of a microcomputer including a CPU 11, a ROM 12, a RAM 13, etc., for controlling and driving a variety of actuators based on various sensor information representative of the operating conditions of the engine 1.
An airflow sensor 17 and a throttle opening sensor 15 are mounted on the intake pipe 3. The airflow sensor 14 measures the amount or flow rate of intake air flowing in the intake pipe 3 and generates a corresponding output signal to the ECU 10. The throttle opening sensor 15 measures the opening of the throttle valve 15 and generates a corresponding output signal to the ECU 10.
The engine 1 is provided with a crank angle sensor 16 and a water temperature sensor 17. The crank angle sensor 16 detects the crank angle or rotational position of an unillustrated crankshaft of the engine 1 and hence the number of revolutions per unit time of the engine 1, and generates a corresponding output signal to the ECU 10. The water temperature sensor 17 detects the temperature of engine cooling water or coolant and generates a corresponding output signal to the ECU 10.
Also, the engine 1 is further provided with an injector 21 for injecting fuel into each engine cylinder, and an ignition plug 22 for electrically igniting the fuel in each engine cylinder. In addition, an intake air control valve 23 is provided in the intake manifold 5 for adjusting the magnitude or momentum of a swirl of intake air sucked into the engine 1.
The CPU 11 in the ECU 10 performs various calculations or operational processing based on the various signals input to the ECU 10 while using control programs stored in the ROM13, determines the operating conditions of the engine 1, and calculates optimal control parameters for various actuators in accordance with the engine operating conditions thus determined.
That is, the ECU 10 controls the valve opening time of the injector 21 so that an optimal amount of fuel is supplied to the engine 1 in accordance with the engine operating conditions. At the same time, the ECU 10 also controls the energization time of an ignition coil so as to provide the ignition plug 22 with optimal ignition timing, and it additionally controls the opening and closing condition of the intake air control valve 23 so as to properly adjust the magnitude or momentum of an intake air swirl.
Next, reference will be made to a concrete processing operation according to the known ignition timing control apparatus for an internal combustion engine shown in FIG. 5 while referring to a flow chart of FIG. 6. FIG. 6 illustrates a control sequence executed by the CPU 11 in the ECU 10.
In FIG. 6, the ECU 10 first reads the number of revolutions per unit time of the engine based on the output signal from the crank angle sensor 16 (step S100), and reads the amount of intake air sucked into the engine 1, based on the output signal from the airflow sensor 14 (step S101).
Also, the ECU 10 determines the operating conditions of the engine 1 based on the information output from other sensors (e.g., the water temperature sensor 17, etc.) in addition to the above-mentioned information input thereto (step S102).
Further, the operating condition of the intake air control valve 23 is determined based on the operating conditions of the engine 1 (step S103), and when it is determined that the intake air control valve 23 is in a closed state, a valve closing flag SCV in the RAM 13 is set to xe2x80x9c1xe2x80x9d (step S104), whereas when it is determined that the intake air control valve 23 is in an open state, the valve closing flag SCV in the RAM 13 is set to xe2x80x9c0xe2x80x9d (step S105).
Subsequently, a determination is made as to whether the valve closing flag SCV is set to xe2x80x9c1xe2x80x9d (step S106), and when it is determined that SCV=1 (i.e., YES), a valve closing condition is established and hence the intake air control valve 23 is driven to close (step S107).
On the other hand, when it is determined in step S106 that SCV=0 (i.e., NO), the valve closing condition is not established (i.e., a valve opening condition is established) and hence the intake air control valve 23 is driven to open (step S108).
Thereafter, an ignition timing xcex8Bc at the closed state of the intake air control valve 23 is stored (step S109), and an ignition timing xcex8Bo at the open state of the intake air control valve 23 is stored (step S110).
Then, a determination is made as to whether the valve closing flag SCV is set to xe2x80x9c1xe2x80x9d (step S111), and when it is determined that SCV=1 (i.e., YES), the ignition timing xcex8Bc at the closed state of the intake air control valve 23 is set as a basic ignition timing xcex8B (step S112).
On the other hand, when it is determined in step SIII that SCV=0 (i.e., NO), the ignition timing xcex8Bo at the open state of the intake air control valve 23 is set as the basic ignition timing xcex8B (step S113).
Subsequently, various correction values such as a water temperature correction factor xcex8WT corresponding to the temperature of engine cooling water detected by the water temperature sensor 17, etc., are calculated (step S114), and a final ignition timing xcex8 is calculated by making various corrections including the water temperature correction factor xcex8WT for the basic ignition timing xcex8B (step S115).
Finally, the ECU 10 drives the ignition plug 22 for each engine cylinder through an unillustrated ignition coil in accordance with a driving routine (not shown) based on the final ignition timing xcex8.
However, in the case where the ignition timing map data are switched in accordance with the opening and closing of the intake air control valve 23, as described above, adverse situations such as, for example, knocking might be caused immediately after the intake air control valve 23 is driven to switch from the closed state to the open state.
That is, even if the intake air control valve 23 is driven to switch from the closed state to the open state to diminish the momentum of the intake air swirl, the existence of a time lag in the change of the intake air swirl momentum might cause knocking when the ignition timing is changed to advance during the period of such a time lag.
Moreover, it may be considered that the ignition timing map data values corresponding to a valve-opened area in the vicinity of a valve-closed area of the intake air control valve 23 are set beforehand to an ignition timing retarded angle side so as to avoid knocking. In this case, however, the performance of the engine 1 might be deteriorated when the engine 1 is driven to run in a steady state in an operating range corresponding to the valve-opened area in the vicinity of the valve-closed area, and it might become impossible to flexibly set the opening and closing areas of the intake air control valve 23.
In the known ignition timing control apparatus for an internal combustion engine, since the ignition timing map data are switched in accordance with the opening and closing of the intake air control valve 23, there exists a time-lag period in the change of the magnitude or momentum of an intake air swirl. Therefore, there arises a problem in that knocking might occur immediately after the intake air control valve 23 is driven to switch from the closed state into the open state when the ignition timing is changed to an ignition timing advanced angle side.
In addition, there is another problem in that even if the ignition timing map data values corresponding to the valve-opened area in the vicinity of the valve-closed area of the intake air control valve 23 are set to the ignition timing retarded angle side in order to avoid knocking, engine performance in the steady state operation would be deteriorated and it would also become impossible to flexibly set the opening and closing areas of the intake air control valve 23, eventually making it impossible to put such an idea into practical use.
The present invention is intended to obviate the above-mentioned problems and has for its object to provide an ignition timing control apparatus for an internal combustion engine which is capable of preventing knocks from being generated immediately after operation of an intake air control valve.
Bearing the above object in mind, the present invention resides in an ignition timing control apparatus for an internal combustion engine, comprising: an engine operating condition detecting element for detecting operating conditions of the engine; an intake air control valve provided in an intake passage of the engine; a swirl control element for controlling the opening and closing of the intake air control valve in accordance with the engine operating conditions detected by the engine operating condition detecting element thereby to adjust a magnitude of a swirl of intake air sucked into the engine; an ignition timing calculating element for determining ignition timing of the engine through interpolation using ignition timing map data corresponding to the number of revolutions per unit time of the engine and an engine load, a map data setting element for switching and setting the ignition timing map data in accordance with opening and closing of the intake air control valve; and an ignition timing retarding element for correcting the ignition timing by a prescribed retarded angle amount over a first predetermined period after a switching of the ignition timing map data. With this construction, the engine is effectively prevented from knocking immediately after operation of the intake air control valve.
In a preferred form of the present invention, when the intake air control valve is changed from its closed state into its open state, the prescribed retarded angle amount is limited in a manner such that retarded ignition timing, which is obtained by subtracting the prescribed retarded angle amount from the ignition timing map data at an open state of the intake air control valve, becomes at an ignition timing advanced side from the ignition timing map data at a closed state of the intake air control valve. Thus, it is possible to prevent not only the generation of knocking immediately after the intake air control valve is driven to operate, but also excessive retarded correction in the ignition timing.
In another preferred form of the present invention, the prescribed retarded angle amount is periodically subtracted to zero by a constant value at intervals of a second predetermined period after a lapse of the first predetermined period. Accordingly, it is possible to suppress not only the generation of knocking but also torque shock immediately after the intake air control valve is driven to operate.
In a further preferred form of the present invention, the ignition timing control apparatus further comprising: a valve opening rate calculating element for calculating a valve opening rate of the intake air control valve; and an ignition timing interpolating element for interpolating the ignition timing map data at an open state of the intake air control valve and the ignition timing map data at a closed state of the intake air control valve in accordance with the valve opening rate when the intake air control valve takes an intermediate opening. Thus, it is possible to prevent the generation of knocking immediately after the intake air control valve is driven to operate, and it is also possible to improve controllability at the intermediate valve opening rate of the intake air control valve.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.